The invention relates to microdialysis probes, embodiments of such probes and to methods for the production or making of such probes.
In medical technology, microdialysis probes are used, for example, to measure concentrations of defined substances dissolved in tissue fluids. A conventional microdialysis probe is typically provided by a probe body and a probe needle protruding from the latter. Upon insertion into a tissue, for example human or animal body tissue, the probe needle is received completely by the tissue and the probe body remains on the surface of the tissue. The probe needle is typically provided with supply and discharge lines, extending concentrically for example, for a perfusion solution, and an area at the end of the supply line has a dialysis membrane. In dialysis, a concentration equalization takes place at the dialysis membrane between the perfusion solution and the tissue environment into which the probe needle has been introduced, and permeable dissolved substances are exchanged. After the concentration equalization, the perfusion solution is returned via the discharge line.
A construction of a microdialysis probe is known from DE 199 37 099 A1, in which the supply line and the discharge line are provided next to one another in the form of separate hollow channels. For this purpose, two tubes are arranged next to one another. The tubes, by the way they are cut, form a common tip for introduction into a tissue and, in an area at which they adjoin, each has an opening to allow the perfusion solution to pass from one tube into the other. A dialysis hollow fiber is arranged inside one tube, and, in the area of the hollow fiber, the tube has recesses in sections for bringing the hollow fiber into contact with the tissue environment. In another embodiment, a star-shaped support structure is introduced into a dialysis hollow fiber. The inner surface of the hollow fiber lies on the tips of the support structure, so that channel passages form between the support structure and the hollow fiber. In an area at the tip of the probe needle, the support structure is interrupted in such a way that the hollow channels are interconnected. One of the hollow channels serves as a supply line for the perfusion solution which, at the transition area of the channels, is passed into the other channels which serve as discharge line.
In the above and other microdialysis probes according to the prior art, an extensive support structure such as a system of tubes is provided, as a result of which a dialysis membrane is not unnecessarily loaded by pressure from the tissue or during penetration into the tissue. The outer surface of the support structure, however, is then, by comparison, much greater than an area left free for dialysis. To achieve a sufficient dialysis surface, the probe needles therefore have to be made correspondingly long and thick. In the case of a support structure in the inside of a dialysis hollow fiber, a dialysis surface is of course considerably increased, but the dialysis membrane does not have sufficient protection against external influences.
In the production of such microdialysis probes, a large number of individual parts have to be fitted into or onto one another, with the result that a large number of transition areas or abutting edges arise between the individual parts, in particular between a dialysis membrane and a support structure. Since the material of a dialysis membrane swells and expands when introduced into a tissue, that is to say when it becomes moist, transition areas between the material of the membrane and the support structure represent weak points of a microdialysis probe. In general, although the material of a dialysis membrane is flexible, it does not automatically remain in a bent or curved shape, and this means that sufficient supporting and securing measures have to be taken to keep a microdialysis membrane in a desired shape. These support structures, however, in most cases severely limit the free dialysis area.